This invention relates to aluminum electrolytic capacitors and more particularly to such capacitors that are packaged in an aluminum can which is closed at one end by a glass-to-metal seal.
Although it has long been recognized that the most hermetic and reliable end seals for electrolytic capacitor packages are glass-to-metal seals, aluminum electrolytic capacitors are essentially always enclosed in an aluminum can which is closed by an end seal comprised of a metal anode tab or wire surrounded by plastic and elastomeric insulating materials. The can itself may provide electrical access to the cathode of the capacitor section.
The prior art attempts at providing a hermetically sealed aluminum electrolytic capacitor have not been successful because no seal glass has been developed to be compatible with the materials of the seal ring and the aluminum capacitor elements and can. Some of the problems of a glass-to-aluminum seal are set forth by Sparrow et al in U.S. Pat. No. 3,522,489 issued Aug. 4, 1970 which discloses an attempt to solve those problems.
Another prior art attempt is shown by Markarian et al in U.S. Pat. No. 3,628,104 issued Dec. 14, 1971 wherein two glass-to-metal seals provide an aluminum electrolytic capacitor section that electrically floats in a sleeve of the same metal that is used for the seal ring. A cylindrical stainless steel casing sleeve is closed at either end by welding it, respectively, to the outer stainless steel rings of the two glass-to-metal seals. The use of two seals avoids the problem of connecting the cathode of the capacitor section to a different metal than aluminum (stainless steel). Such a different metal connected inside the package to the aluminum cathode to eliminate one seal, although weldable to the stainless steel, would be subject to galvanic corrosion and ultimate failure. Also the stainless steel sleeve is readily welded to the stainless steel outer seal ring.
The primary object of this invention is to provide an aluminum electrolytic capacitor enclosed in a true hermetic package using only one hermetic end seal.
It is another object of this invention to provide such a capacitor housed in an aluminum can to minimize cost and to entirely obviate bimetal galvanic corrosion in the electrical connection to the cathode.